Thanks for posting your query.
You are most likely suffering from fungal infection
in groin region which is called as "Tinea Cruris".
Presence of severe itch with red lesion suggests the diagnosis.
You should consult with internal medicine specialist/ dermatologist
and should go for thorough check up.
You should take antifungal ointments
along with oral antifungal
Avoid soap application in affected area.
Wear soft cotton undergarments.
Dr. Mayank Bhargava